Optic fiber shutter apparatus

ABSTRACT

An apparatus for selectively shuttering a light aperture or channel which includes a shutter blade that is rapidly moved by magnetic force between spaced apart end positions. The shutter apparatus maintains the shutter blade stable in either of the two end positions by magnetic attraction, and preferably provides a third stable position for the shutter blade which is intermediate the two end positions, such that the shutter blade has three stable positions corresponding to full, partial and no shuttering of the aperture or channel. In one embodiment, the shutter blade is part of a flag carried by a torsion beam which is fixed at one end in a mount in a cantilever arrangement, and is free to twist about its longitudinal axis. An elongated permanent magnet extends transverse to the flag and presents poles of opposite polarity. An electromagnetic system effects the movement of the elongated permanent magnet, and hence the selective movement of the flag and shutter blade, by attracting and/or repelling the permanent magnet between two end stops. The electromagnetic system includes an E-shaped pole piece of ferromagnetic material which presents three poles. The two outermost poles each have an electrically conductive winding thereon, thereby forming first and second electromagnets. The middle and salient pole is equidistant between the end poles and facilitates the movement of the permanent magnet.

RELATED CASE

This application is a continuation-in-part of U.S. Ser. No. 545,658, nowabandoned, Optic Fiber Shutter Apparatus, filed Oct. 26, 1983.

FIELD OF THE INVENTION

This invention relates generally to devices for selectively shutteringan aperture through which light is to travel, and more particularlyrelates to an extremely small, high speed shutter apparatus for a verynarrow light channel, such as a single optic fiber.

BACKGROUND OF THE INVENTION

It is known in the art to provide a shutter mechanism for moving ashutter blade, or a filter element or other such component, betweenspaced apart first and second end positions by magnetic force. Forinstance, electromagnets have been used to move a shutter blade betweena first position which allows light to pass through an unshutteredaperture, to a second position which prevents the passage of lightthrough the aperture.

Such known shutter mechanisms operate to fully cover or fully uncoverthe aperture, and are not adapted or even desired to provide a thirdposition in which the aperture may only be partly covered (a halfattenuation mode). Further, such prior art devices are ordinarily fairlylarge, and are not designed to operate at a rate of many cycles asecond.

SUMMARY OF THE INVENTION

An advantage of the electromagnetic shutter devices being considered isthat the barest minimum of movable parts are employed in the shutter.For example, a shutter apparatus comprised of a blade carried at one endof an elongated arm which is pivotably mounted for movement betweenopposed electromagnet poles has only one moving part in the form of thepivotally mounted elongated arm. Further, the shuttering operation canbe simply effected by merely exciting the coils of the electromagnets todrive the arm, typically by action on a permanent magnet carried by thearm, thus moving the shutter blade between its two end positions.

It has now been found that such a simple electromagnetic shuttermechanism can be used to particular advantage in applications which callfor the use of an extremely small shutter apparatus that can also beoperated with great rapidity. For instance, it has been found desirableto selectively control the light going to or coming from a single opticfiber element. A practical application for a single optic fiber shutterwould be in a high power light transmission application, such as anoutdoor character image display. Such a display would be comprised of amatrix of pixels formed from single fiber optic elements terminating atone end in expansion or diffusion lenses in a light board display face.The other end of each optic fiber would be arranged in a similar,although much smaller, illumination matrix, with a single independentlyoperable shutter mechanism for each fiber. The entire array of fiberends in the illumination matrix could then be illuminated by a singlelight source with the illumination of each pixel in the display faceeffected by the individual shutters.

Obvious advantages attendant to such a display system are apparent inthe ability to simply control each of a large number of pixels, as wellas the large reduction in power consumed through the use of only asingle source of illumination for the light display, versus thethousands of individual electric lamps which may be used to compose theordinary outdoor display. For such an optic fiber display system tooperate effectively, however, the individual shutter mechanisms must beextremely small, and the power consumed by the multitude of shutteringmechanisms must likewise be quite small. If a "moving" display isrequired very rapid shuttering speeds are necessary, particularly if thedisplay is to generate continuously changing images on the order of areal time picture transmission quality.

It has been a primary object of the invention to provide a simple andefficient shutter mechanism for a light aperture which can effect veryrapid and repeated shuttering operations. Another object of theinvention has been to provide an apparatus for selectively shuttering alight aperture wherein a shutter blade carried on a movable member canbe moved between and retained in spaced apart end positions.

Yet another object of the invention has been to provide a shuttermechanism in a small and compact size, for example, in a size toefficiently and effectively shutter a single optic fiber.

A further object of the invention has been to provide a shuttermechanism with an extremely low energy consumption, on the order ofseveral milliwatt-secs per actuation.

Yet another object of the invention has been to provide a shuttermechanism wherein the moving components are extremely light in weight,and which utilizes a thin flexible member as the shutter blade support,rather than a pivotable shutter blade carrying member. The flexiblemember may be laterally flexible, i.e., bendable between end positions,or in the form of a twistable torsion bar or beam supporting the shutterblade for movement at one end, for example.

A further object of this invention has been to provide a shuttermechanism wherein the shutter blade has three stable positionscorresponding to full, partial and no shuttering of the aperture.

Still a further object of the invention has been to provide an improvedshutter apparatus which includes an E-shaped pole piece or armaturehaving a middle and salient pole which facilitates operation of themechanism.

These and other objects are accomplished in this invention in anapparatus for selectively shuttering a light aperture or channel whichincludes a shutter blade that is rapidly moved by magnetic force betweenspaced apart end positions. The shutter apparatus maintains the shutterblade stable in either of the two end positions by magnetic attraction,and in its preferred form, provides a third stable position for theshutter blade which is intermediate the two end positions, such that theshutter blade has three stable positions corresponding to full, partialand no shuttering of the aperture.

The apparatus essentially comprises, in its preferred form, a memberwhich is movable between two spaced apart end positions which aredefined by stops. A shutter blade is carried by the movable member andis oriented to be interposable between a light aperture or light channelopening and a source of illumination. Permanent magnetic material (e.g.,a permanent magnet) is also carried by the movable member. Anelectromagnetic system effects the selective movement of the movablemember, and hence the shutter blade, by attracting and/or repelling thepermanent magnetic material for movement between the two end stops. Inone mode of operation of the electromagnetic system, the permanentmagnetic material is caused to engage and come to rest against one orthe other of the two end stops, whereupon the shutter blade remains in astable position due to the attraction of the permanent magnetic materialto the ferromagnetic stop. In another mode of operation, theelectromagnetic system causes the permanent magnetic material tomaintain a position between the two end stops, thus providing a thirdstable position for the shutter blade.

In accordance with one embodiment of the invention, the shuttermechanism comprises a flexible elongated member in the form of a thinspring bar or reed which is fixed at one end in a mount in a cantileverarrangement, and is otherwise free to bend laterally. A shutter blade iscarried at the other end of the reed and is thus freely movable in anarc upon lateral flexion of the reed. The permanent magnetic material isan elongated permanent magnet presenting opposed poles of oppositepolarity. The permanent magnet extends transverse to the reed, and ispreferably mounted at a point adjacent the shutter blade.

First and second electromagnets, each including a ferromagnetic corepiece, such as 1% carbon steel music wire, and an electricallyconductive winding thereon, are respectively located on opposite sidesof the flexible reed and spaced therefrom. A portion of the cores ofeach electromagnet extends into the curved path defined by the movementof the permanent magnet, and is preferably covered by an insulating(impact absorbing) bumper thereby defining a respective end stop for thepermanent magnet.

The electromagnetic coils can be excited in one mode to present poles ofthe same polarity adjcent to the poles of the permanent magnet. Thiscauses the permanent magnet to be attracted to one electromagnetic poleand repelled by the other, thereby bending the reed and driving theshutter blade between its two end positions. In another mode, theelectromagnets are actuated to each present a pole opposite to that ofthe nearest pole of the permanent magnet. The permanent magnet isthereby repelled by both electromagnetic poles, causing the permanentmagnet to move to a position between the two electromagnets. The naturalresistance to flexion of the reed thereupon maintains the permanentmagnet in this third stable position between the two electromagnets whenthe electromagnets are de-actuated. The foregoing two modes of selectiveactuation of the electromagnets provides the shutter blade with threestable positions which correspond to full, partial and no shuttering.

In its preferred form, the electromagnetic system includes an E-shapedpole piece of hard (high retentivity, low coercivity) ferromagneticmaterial which presents three poles. The two outermost poles each havean electrically conductive winding on the pole or core, thereby formingfirst and second electromagnets which are arranged and operate aspreviously described. An impact absorbing bumper is located on each polepiece to prevent direct impact of the permanent magnet against the polepiece. The middle (salient) pole is equidistant between the end poles,and generally normal to the path of travel of the permanent magnetcarried by the flexible reed. This middle pole is advantageouslyemployed to direct the streaming magnetic field which would otherwiseexist in the pole piece (through actuation of the electromagnets in alike polarity), and reduce the reluctance of the system. The top or freeend of the middle pole is spaced from the path of travel of thepermanent magnet a sufficient distance so as not to prevent the movementof the permanent magnet between the two end positions. Further, theelongated permanent magnet is sized so that the end poles of thepermanent magnet are each always on an opposite side of the middle pole,and at least slightly laterally spaced therefrom. With this arrangement,the middle pole advantageously cooperates with the two electromagneticouter poles to drive the permanent magnet between the two end positions.

Another embodiment of the shutter mechanism comprises a thin torsion baror beam for the flexible member which carries the shutter blade. Thetorsion bar is fixed at one end in a mount and extends generallyparallel to the elongated poles of the armature. The shutter blade,which is part of a flag, is fixed at the free end of the torsion bar.The flag extends generally perpendicularly from the torsion beam andbetween the two poles which form the end stops of the shutter apparatus.The permanent magnet is carried on the flag. The torsion beam and flagcombination are mounted in a cantilever fashion, with the flag beingreadily moved by the electromagnets.

This second embodiment of the shutter mechanism also advantageously hasthe permanent magnetic material mounted in a recess formed in the bodyof the flag. The ends of the permanent magnet are spaced inwardly fromthe adjacent ends of the recess, so that the material of the flag (e.g.,high impact plastic) serves as an impact absorbing bumper. No bumper istherefore provided on the outer poles of the electromagnetic pole piece,eliminating an assembly step.

A novel housing for the shutter mechanism is also provided in thissecond embodiment which greatly improves the ease of assembly of theshutter mechanism, and yields a compact shutter apparatus which can bereadily employed in use by simply being plugged into a suitable p.c.board.

A particular use of the shutter apparatus of this invention is as ashutter for a single light channel, i.e., a single optic fiber. Suchoptic fibers are well known, being composed of a highly transparentmaterial which is preferably flexible to facilitate its use as a lighttransmitting channel. Clear plastics, such as lucite and plexiglas, areordinarily suitable for such fibers, although flexible glass can also beused. The optic fibers have a higher refractive index than thesurrounding medium to function as a light channel and prevent the lossof light during transmission. Optic fibers come in various sizes; thefibers hereinafter referred to generally will have a diameter of about0.1 inch. The shutter mechanism is accordingly quite small, preferablyfitting within an area of a square on the order of 0.5 inches on a side.It will be noted that as used herein, a single optic fiber implies asingle strand (monofilament) fiber element, as well as a fiber elementsuch as a cable made up of a plurality of strands or filaments formingan optic channel.

In a present application, each of the shutters in combination with asingle fiber optic element forms a pixel, with thousands of such pixelsPG,13 being organized into a matrix array in a display sign board.Because of the small size of these shutters and the efficiency of theshutter mechanism of this invention, an extremely small amount of poweris required for operation of the shutters in such a display board, withthe electromagnets of the shutters operable with currents on the orderof about 250 milliamps in about 0.2 millisecond pulses, for example.Further, the small scale of the shuttering mechanisms permits theorganization of the shutters and fiber ends in an illumination matrixwhich can be illuminated by a single light source. This furtherdecreases the power consumption of the system, since only one lightsource is necessary for such a matrix, and has the salutary benefits ofimproving the maintainability and efficiency of such a display. This isto be compared to display systems utilizing separate incandescent bulbsas the pixels in a similar display, or separate sources of illuminationfor each optic fiber or bundle of fibers.

The small compact size of the shutter as well as its overall operativeefficiency permit the shutter to presently be operated at speeds on theorder of up to 55 operations per second, i.e., movement from one pole toanother. It is thus possible to use such shutters in a fiber optic lightdisplay board in a manner to create a moving light display, withindividual pixels changing faster than the human eye can follow. Such adisplay utilizing the shutters of this invention can providecontinuously changing images on the order of a real time quality videopicture.

The foregoing objectives, features and advantages of the presentinvention will be more readily understood upon consideration of thefollowing detailed description of the invention taken in conjunctionwith the accompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of an embodiment of the shutter mechanism of thisinvention;

FIG. 2 is a cross-sectional view taken along line 2--2 of FIG. 1;

FIG. 3a is a view of the stamping for the shutter blade and flexiblereed as fabricated;

FIG. 3b is a plan view of the shutter blade and flexible reed as formedfor assembly;

FIG. 4 is a perspective view of another embodiment of the shuttermechanism of this invention, partially disassembled for detail;

FIG. 5 is a cross-sectional view taken along line 5--5 of FIG. 4(assembled);

FIG. 6 is a cross-sectional view taken along line 6--6 of FIG. 5; and

FIG. 7 is a detailed view of the flag of this second embodiment.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIGS. 1 and 2, the principal elements of the shutterapparatus of this invention, as illustrated in a first embodiment,comprise a shutter blade 10, permanent magnetic material in the form ofan elongated permanent magnet 11, a movable member in the form of a thinbeam or reed 12 which carries the shutter blade 10 and permanent magnet11, and an electromagnetic system including an E-shaped pole piecegenerally indicated at 13 with electromagnets 14 and 15 formed thereon.The shutter apparatus is particularly adapted for use as a shuttermechanism for a single light channel, such as the single optic fiber 18.One end of the optic fiber 18 is shown here terminating in an aperture16 in a shutter base 17. This end of the fiber is disposed forillumination by a source of light (not shown) which would be directed toilluminate the face of the shutter mechanism as shown in FIG. 1.Although the invention will be described in this particular environmentand on a scale commensurate with this particular application of theinvention, it will be recognized that this invention is not accordinglylimited in size or scope.

The principal object of this invention in its application as a shutterfor the optic fiber element 18 is to provide a simple, effective andreliable shutter mechanism which is of very small size, which isrelatively cheaply and easily manufactured, which is capable of veryrapid controlled cyclic shuttering, which operates on extremely lowpower, and which is durable over an extended period of operation. Thepresent shuttering mechanism is consequently designed with an eyetowards minimizing (a) the number of parts required for assembly of theapparatus, and (b) the power consumed in driving the shutter.

On its most basic level, the shutter utilizes a shutter blade 10 whichis interposable through a magnetic driving force between a source ofillumination and the fiber optic element 18 to thereby cover, uncover,or partially cover the light channel represented by the optic fiber.Light allowed to pass into the fiber 18 is transmitted to the otherterminus of the optic fiber which may be in an expansion lens in asignboard display.

The shutter blade 10 is formed integral with a metal reed 12, as bystamping. Beryllium copper is presently preferred as the metal,primarily for its stiffness and its reduced tendency to interfere withthe magnetic flux pattern set up by the electromagnetic system. 304stainless steel has also been tried as the reed material. Thisparticular stainless steel is mildly magnetic, and it has been foundthat its use in this arrangement further reduces the energy required forshutter operation. The physical mechanism responsible for this resulthas not as yet been ascertained; however, it appears that using a reedcomposed of a material having a tailored magnetic response can enhancethe magnetic circuit used in this shutter mechanism, and thereby furtherreduce the energy consumed in operating the shutter. Other materials,such as plastics, could also be advantageously used for the reedmaterial.

As more clearly shown in FIGS. 3a and 3b, the shutter blade 10 and reed12 are stamped in a single piece from a sheet of beryllium copper havinga thickness of 0.002 inches. The shutter blade is circular, having adiameter of about 0.13 inches which is sufficient to completely eclipsethe face of the optic fiber 18, which here has a diameter of about 0.1to 0.l2 inches. In assembly, the shutter blade 10 is twisted withrespect to the reed 12 so that the plane of the shutter blade 10 isnormal to the plane of the reed 12. The length of the reed is about 0.4inches measured from the point of the twist to other end of the reed,and the reed has a width of about 0.04 inches, giving it good stiffnessto support the shutter blade 10 and permanent magnet 11, but adequateflexibility for lateral movement between the electromagnet 14 and 15.

Also stamped integral with the shutter blade and reed are a pair ofpermanent magnet supporting ears or wings 20a and 20b. Each of the wingsis about 0.075 inches in length and about 0.03 inches in width. Forassembly, the wings 20a, 20b are separated and are respectively bent indifferent directions normal to the plane of the reed 12. This forms asupport surface to which the permanent magnet 11 is attached. It hasbeen found advantageous in this embodiment of invention to locate thewings 20a and 20b and, accordingly, the permanent magnet 11, adjacentthe shutter blade 10 and spaced from the fixed end of the reed.

The permanent magnet material used herein is a magnet made from sinteredAlnico 8 material, 0.094 inches in length and about 0.06 inches indiameter. The relatively small size of the permanent magnet tends tolimit the selection of the various magnetic materials available. It hasbeen found that the most cost effective permanent magnets in this sizerange are sintered magnet materials which are press formed into shape,preferably without machine finishing, e.g., grinding. Alnico 5 andparticularly Alnico 8 materials exhibit excellent B·H energy products insuch a sintered and pressed form.

It will be recognized that although a cunife wire magnet, a ceramicmagnet or a rare earth magnet such as one of samarium cobalt could alsobe used herein, for purposes of economy, the indicated Alnico magnet ispresently preferred.

The magnet 11 presents end poles of opposite polarity in this embodimentof the invention, which for purposes of further description will berespectively described as either north or south poles as indicated inthe figures. The permanent magnet is fixed to the permanent magnetsupporting wings 20a, 20b in a conventional manner, as by gluing.

The entire assembly of shutter blade 10, permanent magnet 11 andflexible reed 12 is mounted for relatively free lateral movement byfixing the end of the reed 12 in a mount 21 in a conventional manner.This cantilever arrangement permits the reed 12 to bend laterallythereby providing arcuate movement to both the shutter blade 10 and thepermanent magnet 11. Mounting of the reed is facilitated in thisembodiment through the provision of a mounting flange 22 which is bentfrom the end of the reed, and which fits into a slot formed in the mount21, being wedged in place.

Movement of the shutter blade 10 between two end positions characterizedby complete covering and complete uncovering of the end of fiber opticelement 18 is effected by magnetic force applied to the permanent magnet11 by the electromagnetic system employed. That is, selective actuationof the electromagnets 14, 15 causes the permanent magnet 11 to beattracted as well as repelled to abut against one of the bumpers 19 oncores 23 or 24 of one of the electromagnets 14 and 15, respectively. Thepermanent magnet thereupon remains in this position even when theelectromagnets are deactuated, due to the attraction of the permanentmagnet to the ferromagnetic core, which may be residually magnetized.

While soft iron (low retentivity material) has been used successfully asa core, it has been found that common carbon (1%) steel, e.g., musicwire, which is annealled at 1000° F. allows faster shutter cycling. The"hard" magnetic core (high retentivity, low coercivity) of carbon steelexhibits hysteresis or residual magnetism, which permits the core to bemagnetized by a very short pulse of current through the electromagnetcoil. The core once magnetized in a given sense (N or S), no longerrequires current flow through the coil to attract/repel the permanentmagnet. The permanent magnet on the shutter reed 12 thus continues to beattracted toward a respective attracting electromagnetic pole even afterthe actuating current pulse has stopped, permitting greater cyclingspeed for the shutter.

The preferred electromagnetic system used herein comprises an E-shapedpole piece 13 of 1% carbon steel which presents two outer poles 23 and24 which form the cores for the electromagnets 14 and 15, respectively,and a middle salient pole 25. Each of the outer poles has an excitingcoil 26, 27 thereon which consists of an electrically conductive windingon bobbins 28, 29. A winding of 2,000 turns of #32 copper wire has beenused to advantage herein. Each of the pole pieces is of a sufficientheight so that a portion of the core 23, 24 extends into the path oftravel of the permanent magnet 11. Bumpers 19 surround these portions ofthe cores, and form the respective end stops for the permanent magnet11, and therefore define the end positions 30a, 30b (shown in brokenline in FIG. 1) for the shutter blade 10. The use of end stop bumpers19, which may be made of a suitable impact absorbing plastic or rubbermaterial, with hard magnetic core materials with low coercivity (such asthe 1% carbon steel), prevents the moving permanent magnet fromdemagnetizing or remagnetizing the core.

In this embodiment, the outermost poles are about 0.5 inches apart,measured center to center on the cores, and the middle pole 25 isequidistant between the two poles. The diameter of all of the polepieces is approximatel 0.050 inches. It will be noted that the middlepole 25 is slightly offset from a center line running between the twooutermost poles so that the middle pole 25 is substantially normal tothe center of the arcuate path of travel of the permanent magnet 11. Thecenter pole 25 is also shorter than the outer poles, a condition whichwill be hereinafter discussed in more detail. It may, nevertheless, benoted at this point that the gap between the top of the center pole 25and the bottom of the permanent magnet 11 is equal to approximatelyone-quarter of the distance between the two outer poles, which in thisembodiment is a gap distance of about 0.1 inch.

The ends of the poles of the pole piece 13 extend through aperturesprovided in the base 17 in a snap type fit. The base is advantageouslyformed of plastic and is injection molded. A contoured recessed area 31is formed in the base in which the reed 12, permanent magnet 11 andshutter blade 10 are received. The pole pieces 23 and 24 may be furtherelongated to provide the means for attaching the shutter mechanism in amatrix formed on a printed circuit board 33.

The exciting coils 26, 27 of the electromagnets can be connected to eachother in series alone if a bi-stable shutter is only required, orpreferably in a manner to provide for independent operation of eachelectromagnet. This latter arrangement will be the one particularlydescribed herein.

The coils 26, 27 are connected to a common source of current by means ofa control system which determines whether the coils are to be excited soas to induce like poles in the ends of the core pieces adjacent thepermanent magnet (N, N, or S, S) or opposite poles (N, S or S, N). Thecontrol system also determines the length of time during which the coilsare excited.

In operation as a tri-stable shuttering apparatus, that is, an apparatusin which the shutter blade 10 is to occupy end positions correspondingto complete shuttering of the fiber optic element 18 or completeuncovering of the fiber optic element 18, and a third stable positionpartially covering the fiber optic element so as to give a half-toneimage, the coils 26, 27 of the electromagnets 14, 15 would be excited asfollows. Without any electromagnetic force acting on the permanentmagnet, the normal rest position for the shutter blade 10 would bebetween its two end positions 30a, 30b. This is due to the naturalresistance of the reed 12 to flexion. In this position, the shutterblade 10 overlies a portion (approximately half) of the optic fiber end18, which produces a half-tone or half attenuation of the light beingtransmitted by the optic fiber to a terminus in a lens in a lightdisplay board.

Given the orientation of the poles of the permanent magnet 11 aspreviously indicated, in order to drive the shutter blade 10 to aposition (30b) fully covering the fiber optic element end 18, both ofthe coils would be excited so as to induce north poles at the ends ofthe pole pieces 23 and 24. The north pole of the permanent magnet 11would accordingly be repelled by the north pole of electromagnet 14,while the south pole of the permanent magnet 11 would be attracted tothe north pole of electromagnet 15. The stray field of the permanentmagnet 11 is sufficiently strong so that the magnet remains in thisposition due to attraction between the permanent magnet and the core 24of the electromagnet, which in this embodiment will further have aresidual attractive polarity. The optic fiber end 18 is therebycompletely covered by the shutter blade 10.

If it is desired to fully expose the fiber optic element 18 toillumination (position 30b of shutter 10), the process is reversed sothat the coils 26, 27 of the electromagnets are excited to produce southpoles adjacent the ends of the electromagnets 14, 15, thereby repellingthe permanent magnet from core 24 while attracting the north pole of thepermanent magnet to core 23 of electromagnet 14. Again, the magneticattraction between the permanent magnet 11 and the core 23 of theelectromagnet maintains the shutter blade 10 in this fully uncoveredcondition.

Magnetic insulation (not shown) may also be provided surrounding theshutter mechanism to prevent spurious external magnetic interferencewith the operation of the shutter.

The permanent magnet 11, and therefore the shutter blade 10, is causedto maintain a third stable position between the two end positions byexciting the coils of the electromagnets so that the permanent magnet isrepelled away from each end position. Again referring to the arrangementherein, the coil 26 of electromagnet 14 is excited so as to induce anorth pole adjacent the north pole of the permanent magnet 11, and thecoil 27 of electromagnet 15 is pulsed to produce a south pole adjacentthe south pole of the permanent magnet. The permanent magnet 11 wouldtherefore occupy a position between these repelling magnetic forceswhich would be maintained even when the coils are deactuated due to thenatural resistance to flexion of the reed 12. Of course, when hardmagnetic core material is used, the centering forces are present evenwhen the current does not flow, because of the residual magnetisminduced in the two pole pieces and the salient middle pole.

The middle and salient pole 25 of the E-shaped pole piece is provided totake advantage of the streaming magnetic field which would ordinarilyexist in its absence, where like poles of like polarity are induced atthe ends of the two outermost poles. The salient pole 25 reduces theoverall reluctance of the magnetic system, and in this arrangement it isalso advantageously employed to enhance the magnetic force being appliedto move permanent magnet 11.

The permanent magnet 11 and the E-shaped pole piece 13 are cooperativelysized so that the polar ends of the permanent magnet 11 always remain onopposite sides of the middle pole 25, and are slightly spaced therefrom.That is, with the north pole of the permanent magnet 11 abutting againstthe bumper 19 of core 23 of electromagnet 14, the south pole of thepermanent magnet 11 is on the opposite side of the center pole 25, withthe end slightly spaced from that side. Likewise, the north pole of thepermanent magnet will be spaced from the center pole 25 with the southpole of the permanent magnet abutting against the core 24 of theelectromagnet 15. Taking the example where it is desired to move thepermanent magnet from a rest position against the bumper 19 of core 23(full uncovered, 30a) to a rest position against the bumper of core 24(fully covered, 30b), north poles would be induced in the ends of thepole pieces 23 and 24. A south pole would accordingly be induced in thesalient pole 25. This south pole would repel the nearby south pole ofthe permanent magnet, thereby driving it towards core 24, while alsoattracting the north pole of the permanent magnet, further contributingto the movement of the permanent magnet. It will of course be recognizedthat the same operation would work in reverse in moving the permanentmagnet from rest against bumper 19 of core 24 to abut against bumper 19of core 23.

It has been found in the practice of this invention that the center pole25 must be spaced a sufficient distance from the permanent magnet toavoid counteracting the effects of the two electromagnets. This distancewill of course var with the relative strengths of the electromagnets,the permanent magnet, and the shape of the permanent magnet. In thisembodiment, the gap distance is about 0.1 inch. It may also be notedthat, in general, the ratio between the length of the permanent magnetto its diameter (or width) should be in the range of from 1:1 to 4:1 to(maximize the effectiveness of the magnet.

Another embodiment of the shutter apparatus of this invention isillustrated in FIGS. 4-7. Like the previous embodiment, the shutterapparatus generally comprises a shutter blade, here in the form of aflag 50, an elongated permanent magnet 51, an electromagnetic systemincluding an E-shaped pole piece or armature generally indicated at 52having electromagnets 53 and 54 formed thereon, and a movable member,here in the form of a thin torsion bar or beam 55 which carries the flag50 at one end. This shutter apparatus is also particularly adapted foruse as a shutter mechanism for an optic channel represented by theaperture 58 in FIG. 4.

The torsion beam 55 is formed from a phosphorous bronze sheet materialof spring temper about 0.002 in. thickness; it could also be made of thesame beryllium copper as the shutter blade and reed 10, 12 of theprevious embodiment. The torsion beam 55 is approximately 0.963 in. longand is formed into an L having perpendicular sides approximately 0.02in. in width. One end of the torsion beam 55 is fixed in a mount 62(FIGS. 5 and 6) which is part of a shutter case made up of a base 63a acover 63b and a socket portion 63c. The flag 50 is fixed to the free endof the torsion beam 55, with both the flag 50 and torsion beam 55suspended in cantilever fashion.

The flag 50 (FIG. 7) is a single piece molded plastic element having anaperture covering blade 64, a body portion 65 and a base 66. A recess 67is formed in the body 65 of the flag, and receives the permanent magnetmaterial 51 therein. The flag itself is approximately 0.638 in. inlength from end to end, with the blade 64 having a diameter of about0.16 in. The permanent magnet 51 is located about 0.3 in. from the axisof the torsion beam 55. It is a sintered Alnico material about 0.1 in.long and about 0.068 in. in diameter.

The torsion beam 55 is received in a socket formed in the base 66 of theflag 50, and is fixed therein. The flag 50 extends generallyperpendicular from the torsion beam 55, and is located between outerpoles 69 and 70 of the armature 52, such that the permanent magnet 51 isabout equidistant between the two poles 69, 70 in its rest position. Tothis end, torsion beam 55 is mounted to extend generally parallel to thearmature 52 along a midline between the two poles 69, 70. The E-shapedarmature 52 is completed by a middle or salient pole 71. Outer poles 69,70 form the end stops for the flag 50.

The electromagnetic system employed in this embodiment is generally thesame as that previously described. The armature 52 is preferably formedof a single piece of music spring quality steel wire which is bent intothe E-shaped pole piece. The preferred steel wire for the armatureconforms to ASTM A228, with a diameter of about 0.048 in. A distance ofabout 0.3 in. as measured between the middles of the outer poles 69, 70is provided in this embodiment.

The electromagnets 53, 54 have exiting coils or windings 72a, 72b,respectively, each of 1200 turns of No. 36 magnet wire. The windings72a, 72b are wound on plastic bobbins 74, 75. Mounted at one end of eachof the bobbins are a pair of stiff wire connectors 76a, 76b, which formthe electric terminals for the coils. The connectors 76a, 76b arereceived in conductive terminals 77a, 77b provided in the socket portion63c of the casing, and have conductive pins 78a, 78b extending outwardlytherefrom. The entire electromagnetic system is thus easily fabricated,and readily assembled with the rest of the apparatus by simply slidingthe connectors 76a, 76b into the coil terminals 77a, 77b. Each of theshutter apparatuses is in turn readily mounted, such as in a pc board,by simply inserting the pins 78a, 78b into appropriate sockets therein.

Although not shown herein, steering diodes can be provided in thecircuitry of the electromagnets to prevent cross-path currents from oneshutter mechanism from acting on an adjacent shutter apparatus, such asmight occur in row scanning circuitry used in a multiplexing mode.

It will be noted that the permanent magnet 51 is sized slightly smallerthan the recess 67 of the flag in which it is received. The ends of thepermanent magnet 51 are thus spaced slightly inwardly from the lateralsides of the flag 50 which define the recess ends. The plastic materialof flag 50 thus serves to absorb the impact when the flag 50 strikes oneof the outer poles 69, 70. This takes the place of the bumpers 19provided on the outermost poles of the previously described embodiment.

Since the operation of the second embodiment of the shutter apparatus isidentical to that previously described, it will therefore not berepeated.

Another feature of the second embodiment of the shutter apparatus is thecompact casing in which the shutter mechanism is mounted and contained.As previously indicated, the casing is formed of a base part 63a, acover part 63b and a socket portion 63c. The three parts 63a, 63b and63c are all plastic molded to snap fit together for ease of assembly ofthe shutter apparatus, with the socket portion 63c sliding over theoutside of parts 63a and 63b to form a compact and sturdy unit for theshutter apparatus. A flange 80 on socket portion 63a extends through aslot 81 provided in cover part 63b. The flange 80 serves as a fingergrip for manipulating the shutter mechanism.

The shutter casing also advantageously includes two ferrules 83, 84which receive respective ends of two optic fibers 85, 86 making up thelight channel. Input ferrule 83 receives an end of an optic fiber 85carrying light from a source of illumination (not shown). The fiber 85terminates adjacent end 83a of the input ferrule. A second optic fiber86 in output ferrule 84 then carries light from the input fiber 85 to aterminus in an optic display, e.g., a diffusion lens or the like.Aperture 58 is essentially the end of optic fiber 86. A small gap thusexists between the aperture 58 and the input ferrule end 83a withinwhich blade 64 of the flag 50 moves to effect shuttering of the lightchannel. Use of the ferrules 83, 84, which can be molded with theshutter casing parts, permits the optic fibers 85, 86 to be readilyattached to the shutter apparatus in proper alignment. Harnesses (notshown) applied to the ends of the optic fibers 83, 84 further facilitateassembly.

Because of the extremely small size of the shutter mechanism, the smalldistance of travel of the permanent magnet to the electromagnetic poles,and overall efficiency of the mechanism, very little energy is requiredto operate the shutter. Currents on the order of about 250 milliampshave been effectively used in these embodiments. With the resistance ofthe electromagnetic circuit of the first embodiment about 65 ohm d.c.per coil (inductance about 22 millihenries), pulsing the current atabout 0.2 milliseconds a pulse yields an energy consumption of about1.22×10⁻³ watt-sec., which is an extremely small energy requirement foreffective operation of the shutter. Even shorter drive pulses can beobtained by winding lower resistance (e.g., fewer turns of heavier wire)coils having lower resistance and inductance. A great number of suchshutters can consequently be operated off of a lower power source.

As noted herein, the particular application of this shutter mechanism isas a shutter for a single fiber optic element forming a pixel in a lightdisplay matrix having a multitude of such fiber optic elements. The sizeand performance of the shutte mechanism enables extremely rapidoperation of the shutters, with shuttering sequences of about 80operations per second being presently achieved. It is thus contemplatedthat an extremely large array of such pixels can be organized andcontrolled in a large light display, such as an outdoor sign board,which can be operated in a manner so as to produce images changing in areal time picture display. The shutter mechanism is also quite durable,having a lifetime calculated to be in excess of 10⁸ operations, andverified to 10⁸ in prototypes.

The relatively simple fabrication of the various components of theshutter mechanism in relatively low cost materials along with the easyassembly of the various components further enhances the utility of thisshutter.

Thus, while the invention has been described in connection with acertain presently preferred embodiment, it will be immediately obviousto those skilled in the art that many modifications of structure,arrangement, portions, elements, materials and components can be used inthe practice of the invention without departing from the principles ofthis invention. For instance, the foregoing description of the inventionemploys a permanent magnet carried by the reed/flag to effect movementof the reed/flag and therefore the shutter blade. It is neverthelesswithin the scope of this invention to simply attract a ferrousreed/flag, or a reed/flag carrying some magnetic (e.g., ferrous)material, for movement of the shutter blade between the end positions.When unattached to one or the other of the electromagnetic poles, thereed/flag would occupy a third stable position between the endpositions. More power would of course be required to magnetically holdthe reed/flag in either of the end positions in this arrangement, butthis may be offset by other advantages in applying the invention in thismanner.

What is claimed is:
 1. A shutter mechanism comprising:a mount, a torsionbeam having a longitudinal axis about which it twists, the torsion beambeing fixed at one end to the mount, a flag fixed to the torsion beam ata point spaced from said fixed beam end, the flag having a shutter bladeportion formed thereon, a permanent magnet carried on the flag, firstand second electromagnets for attracting and repelling the permanentmagnet, each electromagnet including a ferromagnetic core piece and anelectrically conductive winding thereon, the first and secondelectromagnets respectively located on opposite sides of the flag, aportion of the core of each electromagnet extending into a path of thepermanent magnet defined by the rotation of the permanent magnet aboutsaid longitudinal axis when the torsion beam twists, selective actuationof the electromagnets causing the flag to engage and come to restagainst one of the core pieces of the electromagnets with the permanentmagnet maintaining this engagement upon deactuation of theelectromagnets in one mode of operation, and causing the permanentmagnet to maintain a third stable position between the twoelectromagnets in another mode of operation, whereby the shutter bladecarried on the flexible member has three stable positions correspondingto full, partial and no shuttering.
 2. A shutter mechanism comprising:amount, a torsion beam having a longitudinal axis about which it twists,the torsion beam being fixed at an end to the mount, a shutter bladecarried by the torsion beam, and means for twisting said torsion beamfrom a rest and first position to a second and twisted position, wherebythe shutter blade selectively covers and uncovers an aperture throughoperation of the twisting means.